Poweder metal compacts



United States Patent POWDER METAL 'COMPACTS Application November 14, 1955 Serial No. 546,830

1 Claim. (Cl. 75-200) No Drawing.

This invention relates to the production of powder metal compacts and is more particularly concerned with the production of such compacts from stainless steel powder.

In the production of powder metal compacts two general procedures are adopted comprising the steps of compressing and heating, a mixture of metal powders together with suitable lubricants being compressed in a mould or die to form a green compact which is then heat-treated or sintered at a suitable temperature to develop the full properties of the material.

It will be appreciated that prior to sintering some handling (mechanical or manual) of the green compact is necessary, and since stainless steel powder tends to produce compacts of a brittle nature, there is a liability of edges and corners being severely damaged. Moreover stainless steel powder is extremely difficult to compact and requires the application of very high pressing loads which cause excessive die wear to'occur.

It is therefore an object of the present invention to minimise the drawbacks mentioned by increasing the strength of green compacts made of stainless steel powder.

According to this invention in the production of powder metal compacts, stainless steel powder has added thereto a quantity of fine nickel powder with a suitable lubricant.

According to a feature of the invention the stainless steel powder is mixed with from 5 to 30% of fine nickel powder, 1% of paraffin Wax and 030m 0.7% of calcium stearate. The particle size of the nickel powder should be small, preferably passing through a 300 mesh sieve.

As an example a normal stainless steel powder of the following composition:

and of particle size distribution in the limits:

ice

Percent mesh B. S. S Nil -100+200 mesh B. S. S 75-85 -200+300 mesh B. S. S 5-15 300 mesh B. S. S 5-15 lubricated with 1% paraffin was added (in a solvent) and 0.3% calcium stearate, was compacted at 35 tons per square inch. The resultant green compact had a density of approximately 6.3 grams per cubic centimetre. The compact when sintered at 1300 C. for one hour had a tensile strength of 22 tons per square inch, a 3% elongation, a hardness of to V. P. N. and a density of 6.37 grams per cubic centimetre.

When however according to the invention 20% nickel powder (smaller than 300 mesh B. S. S.) was added to the aforesaid normal composition and compacted under the same conditions, the resultant green compact had an increased density of 6.7 grams per cubic centimetre, giving adequate strength for handling prior to sintering.

After sintering at 1300 C. for one hour the compacts had a tensile strength of 26 tons per square inch, a 7% elongation, a hardness of to V. P. N. and a density of 7.1 grams per cubic centimetre. The sintered compacts were found to be resistant to boiling dilute nitric acid, thus establishing that sufiicient diffusion of the fine nickel powder in the stainless steel composition had occurred during sintering to ensure that the compacts were essentially stainless. Further, the addition of fine nickel powder was found to have a remarkable elfect upon the compressibility of the powder mixture, enabling higher densities to be obtained at lower compacting loads.

What we claim is:

The method of producing powder metal compacts from stainless steel powder for increasing the strength of the unsintered compact and for providing a sintered product of greater tensile strength and hardness, the

steps comprising adding suflicient nickel powder of aparticle size smaller than 300 mesh to stainless steel powder having a normal nickel content of 7-10% to increase the nickel content of the stainless steel powder to 12-40%, compressing the mixture of metal powders together to form a firm compact and sintering the compact at a suitable temperature to develop the full properties of the compact.

References Cited in the file of this patent UNITED STATES PATENTS 2,214,104 Hildabo1t et al. Sept. 10, 1940 2,377,882 Hensel et a1. June 12, 1945 2,677,610 Evans May 4, 1954 2,801,916 Harris et a1. Aug. 6, 1957 FOREIGN PATENTS 424,282 Great Britain Feb. 18, 1935 625,397 Great Britain June 27, 1949 

